Mixed-resin mantle metal-core golf balls and methods of manufacturing same

ABSTRACT

A golf ball is provided. The golf ball includes a hollow metal core made from a work-hardened metal alloy. The golf also includes a mantle layer enveloping the metal core. The mantle layer may be made from a mixture of long-ball resin and soft-ball resin. The golf ball further includes a cover positioned about the mantle layer to protect the mantle layer. A method of manufacturing the golf ball is also provided.

TECHNICAL FIELD

The present invention relates generally to metal core golf balls, and more particularly, to multi-sphere golf balls having a hollow metal core.

BACKGROUND ART

Currently, there are a myriad of commercially available golf balls. However, in order to meet the United States Golf Association (“U.S.G.A.”) specifications, the golf ball must be, among other things, spherical in shape, have equal aerodynamic properties, and equal moments of inertia about any axis through its center. In addition, the golf ball must have a minimum diameter of 1.68 inches (4.267 centimeters), a maximum weight of 1.620 ounces (45.926 grams), and a maximum initial ball velocity of 255 feet per second as measured on a standard U.S.G.A. ball-testing machine. There is also a maximum carry distance of 325 yards, again using the U.S.G.A. standard test machine.

The basic concept of the modern golf ball is the invention of Coburn Haskell and Bertram Work in 1898 at the B.F. Goodrich Co. of Akron, Ohio. The concept, as disclosed in U.S. Pat. No. 622,834, includes compressing a rubber inner core by wrapping it with an elastic thread or tape. The compression of the core results in a much higher coefficient of restitution (COR) when the ball is struck with the club head. A design-around of the U.S. Pat. No. 622,834 resulted in the replacement of the solid rubber core with a rubber pressure vessel containing compressed air. U.S. Pat. Nos. 707,263 and 785,184 to A. T. Saunders disclose a pneumatic golf ball whereby the pressure vessel was wrapped in latex-impregnated cotton or silk thread. The Saunders patents were acquired by the Goodyear Tire & Rubber Company and produced in the period prior to World War I. In its commercial embodiment, the pressure vessel was provided with about 800 psi of compressed air. Although the product produced excellent results in play, it was discontinued due to an unfortunate tendency towards catastrophic structural failures in mid-flight.

Further development of hollow-cored golf balls was delayed until the introduction of synthetic polymers, which removed the need for wrapped-pressurized cores. Examples of such hollow-cored polymer golf balls are provided in U.S. Pat. No. 5,980,395. These hollow-cored balls were designed to include a polybutadiene (specific gravity 0.92), to which a tungsten or similarly dense filler was added to increase the specific gravity. It should be appreciated that golf balls having specific gravities of about 2 g/cm³ are typically reported as being practical.

As golf ball technology advanced, golf balls with a metal hollow core were introduced. A metal hollow-cored golf ball having a polybutadiene mantle is described in U.S. Pat. Nos. 6,004,225, 6,976,925 and 705,957 to Owens et al. These Owens et al. patents disclose specifically, the use of titanium cores, and disclose generically, the use of carbon steel, nickel, molybdenum, tungsten and aluminum, and alloys thereof.

In general, a hollow core golf ball permits placement of more of the mass of the ball in its periphery, thus resulting in a substantially higher moment of inertia (MOI). The advantages of increased MOI are well known in the art and are provided in the Owens patents.

For most conventional golf balls, the core and mantle includes the incorporation of polybutadiene. However, the Owens patents disclose alternatives to the polybutadiene mantle of the metal-cored golf ball. These alternatives include synthetic rubbers, such as polyisoprene and styrene-butadiene. Other alternatives to polybutadiene have been disclosed in U.S. Pat. Nos. 6,100,321, 6,777,472 and 6,815,480, and in U.S. Publication No. 2005/0148525 to J. C. Chen and R. J. Statz et al., all of which are assigned to E.I. du Pont de Nemours and Company (“DuPont”). These highly complex thermoplastic resins include mixtures of: salts of ethylene/methylacrylic acid/butylacrylic acid “random” terpolymers (Surlyn®), magnesium stearate, and terpolymers of butylene/polyalkylene ether/phthalic acid diester (Hytrel®) mixed with ZnO. Mixtures of Surlyn®, Hytrel®/ZnO and magnesium stearate are marketed by DuPont for use in the manufacture of golf balls as High Performance plastics under the trade name “HPF.” For lack of an art-recognized generic name for such resins, these resins are hereinafter referred to as SHS resins.

Those skilled in the art can appreciate that golf ball polymers can be effectively characterized by two parameters: (1) the coefficient of restitution (“COR”), which is measured by firing a ball at a steel plate at 125 ft/sec and measuring the rebound velocity, and (2) the Atti compressibility or PGA compressibility (“Comp”), which is measured by the force needed to compress the ball. In general, a harder ball has a relatively larger Comp than the softer ball. The numerical relationship between the composition of HPF and its COR and Comp are described in U.S. Publication No. 2005/0148725 to Statz et al. Presently, there is commercially available a DuPont product marketed under the name HPF 2000® as a replacement for polybutadiene. The manufacturer reports a COR of 0.828 and Comp of 91 for HPF 2000® neat spheres (˜1.52″ O.D.).

The design of golf balls and materials for their construction generally requires a balance of the material resilience (i.e., the spring-like ability per unit volume to absorb stress energy without structural failure), elasticity (i.e., the ability to reflect (absorb and release) energy without hysteresis loss), and compressibility (i.e., the ability to undergo reversible deformation in response to pressure). It should be noted that material resilience and elasticity can allow for efficient transfer of energy from club head to ball. In general, when the ball is resilient and elastic, the initial velocity of the ball can typically be about 50% greater than the velocity of the club head. As such, the ball speed to head speed ratio (B/H ratio) can be 1.5. Highly compressible (easily deformable) balls, on the other hand, can be more satisfactory in the short game and more readily controlled. Golf balls that are not as compressible and feel like stones or steel ball bearing golfers are often shun.

Accordingly, it would be desirable to provide a golf ball that can consistently display an optimum balance of material resiliency, elasticity and compressibility.

SUMMARY OF THE INVENTION

The present invention provides, in one embodiment, a golf ball having a metal core made from a work-hardened metal alloy, for instance, American Iron and Steel Institute (AISD type 301 stainless steel. In an embodiment, the metal core may be a hollow core made from two substantially similar hemispheres welded to one another. The golf ball also includes a mantle layer enveloping the metal core. In an embodiment, the mantle layer includes a mixture of a long-ball resin, for instance HPF 2000, and a soft-ball resin, for instance AF 1035, so as to provide material resiliency, elasticity and compressibility. The golf ball further includes a cover positioned about the mantle layer, so as to protect the mantle. In an embodiment, the cover may include an aerodynamic pattern imprinted thereon.

The present invention also provides, in another embodiment, a method for manufacturing a golf ball. The method includes initially providing a metal core made from a work-hardened metal alloy. In an embodiment, the core may be made from two substantially similar hemispheres stamped from the work-hardened metal alloy. Next, the metal core may be enveloped with a mantle layer made from a mixture of a long-ball resin and a soft-ball resin. Thereafter, a cover may be placed about the mantle layer, so as to protect the mantle layer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a cross-sectional view of a golf ball of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

As noted above, the design of golf balls and materials for their construction generally requires a balance of the material resiliency, elasticity, and compressibility, so as to allow for efficient transfer of energy from club head to ball, while provide better control.

Looking now at FIG. 1, there is illustrated a golf ball 10 in accordance with one embodiment of the present invention. Golf ball 10, as illustrated, includes a metal core 11. In an embodiment, metal core 11 may be a hollow core fabricated from two substantially similar hemispheres affixed to one another. Affixation, as it should be appreciated, can be by welding or by any other means known in the art, so long as the hemispheres can remain securely affixed to one another. In addition, as the strength, ductility and resiliency of the sphere can be critical, the metal core 11 may be made from a strong material. Examples of a suitable material include an austenitic alloy, or any material that meets the specification for the American Iron and Steel Institute (AISI) type 301 stainless steel.

In one embodiment of the invention, such a material may include a combination of iron, nickel, chromium, carbon, silicon and manganese. In a specific embodiment, the material may include iron, about 6-8(w/w) % nickel, about 16-18(w/w) %) chromium, and at most about 0.15(w/w) % carbon, about 1(w/w) % silicon and about 2(w/w) % manganese. This type of stainless steel, of course, may be available with varying degrees of hardening and can undergo rapid hardening when worked. As an example, quarter-hardened type 301 stainless steel represents a good compromise between ductility, and hence stamping speed, and the mechanical properties of the final product. Those skilled in the art may appreciate that type 301 stainless steel can readily work-harden when cold stamped. Moreover, type 301 stainless steel can be available in different thicknesses. Accordingly, the degree of work-hardening, and hence resiliency, can be affected by alteration of the initial thickness of the metal sheet stock and the initial state of hardening. However, satisfactory results can be achieved using a stock which is commercially available as quarter-hardened having similar thickness as that desired for the finished product.

In addition to the material from which the metal core 11 may be made, the dimensions of metal core 11 may affect the performance of golf ball 11. To that end, metal core 11, in an embodiment, may be designed so that its dimensions can provide a sufficient balance between the coefficient of restitution (“COR”), and compressibility (“Comp”) in the resulting golf ball 10. Generally, as diameter D of the core 11 increases, both the COR and Comp of the golf ball 11 also increase. In accordance with one embodiment, metal core 11 may be provided with an outside diameter D ranging from about 0.90″ to about 1.150″. Moreover, should it be necessary, thickness of the finished metal core 11 can be adjusted, so that the weight of the finished ball can be within USGA limits, that is, not more than 1.62 oz.

Still referring to FIG. 1, golf ball 10 may also include a mantle layer 12 enveloping metal core 11. It should be appreciated that the material from which the mantle layer 12 may be made can affect the performance of golf ball 10. As such, a material with a substantially high coefficient of restitution (COR) may be used in order to obtain maximal carry distance. However, should the material provide golf ball 10 with a compressibility characteristic that is significantly large, the golf ball 10 may be subjectively unacceptable to a player who may perceive that the golf ball 10 lacks feel, and thus less suitable for the short game. In one embodiment of the invention, a resin material with the appropriate COR and Comp may be used. In order to determined whether the resin material used has the appropriate COR and Comp, the properties of, for instance, neat spheres of the resin may be measured in the size of golf balls by USGA recognized techniques.

The mantle of golf balls, at present, are generally constructed from a synthetic rubber, such as polybutadiene, which can be used with metal-core balls similar to the golf ball 10 of the present invention. However, polybutadiene can give less than satisfactory durability. Synthetic polymer resins having a mixture of an ethylene methylacrylic acid ionomer (Surlyn®), and an alkylene etherester terephthalic acid polymer (Hytrel®) mixed with ZnO and magnesium stearate have been developed specifically for certain golf ball manufacture. A resin material having these ingredients are hereinafter referred to as a Surlyn®/Hytrel®/magnesium stearate resin or SHS resin. An example of an SHS resin optimized for maximum carry distance is HPF 2000 from DuPont®. The COR and Comp of this resin for a minimum 1.68″ (i.e., neat sphere) diameter regulation golf ball have been reported to be about 0.826 and about 91. HPF 2000 and other SHS resins having a neat sphere COR of at least 0.820 and Comp of at most 93 are usually referred to as “long-ball SHS resins.”

It should be noted that a mantle layer that is made solely of HPF 2000 or other long-ball SHS resins provides optimal carry distance, but also provides a ball that would be perceived by many as hard or lacking “feel.” SHS resin have also been optimized for control. An example of such an SHS resin is AD 1035. However, a mantle layer that is made solely of AD 1035 or other “soft-ball SHS resin” can give a golf ball a noticeably compromised carry distance.

To that end, the mantle layer 12 of golf ball 10, in one embodiment of the presenting invention, may include a long-ball SHS resin or mixture of long-ball SHS resins, along with a soft-ball SHS resin or mixture of short-ball SHS. In an embodiment, mantle layer 12 may be fabricated to include a ratio of about 1:1 mixture of long-ball and soft-ball SHS resins. In another embodiment, the mantle layer 12 of the golf ball 10 can include a mixture of long-ball and soft-ball SHS resins in ratios of from about 2:1 to about 2:3, so as to display a carry distance that is substantially the same as the pure long-ball mantle, while having noticeably improved “feel.” In one embodiment, the amount of soft-ball SHS resin may be relatively higher than the amount of long-ball SHS resin, such that any ratio of long-ball SHS resin to soft-ball SHS resin may be use, so long as the amount of soft-ball resin is relatively higher than the amount of long-ball resin, while not compromising the carry distance and the desired “feel”.

Golf ball 10 further includes a cover layer 13 situated about the mantle layer 12. The cover layer 13, in an embodiment, can act to provide protection to mantle layer 12. To that end, the cover layer 13 may be made from, for example, Surlyn® or any art-recognized substitute. The cover layer 13 may also be a textured material, made from an ionomer, and onto which an aerodynamic pattern can be imprinted. In an embodiment, the cover layer 13 may be provided with a thickness ranging from about 0.05″ to about 0.75″.

To manufacture golf ball 10 of the present invention, a metal core 11 may initially be provided. In one embodiment, metal core 11 may be formed by cold stamping from any material that meets the specification for the American Iron and Steel Institute (AISI) type 301 stainless steel into, for instance, two substantially similar hemispheres. Since quarter-hardened type 301 stainless steel can represent a good compromise between ductility, hence stamping speed, and the mechanical properties of the final product, it may be a material of choice for the metal core. After stamping, the metal hemispheres may be welded to one another by conventional means. Although the use of two hemispheres is disclosed, it should be noted that more than two stamped pieces may be welded to one another to form the metal core 11.

Next, mantle layer 12 may be formed about the metal core 11. In an embodiment, a mixture of long-ball SHS and soft-ball SHS may be injection molded about core 11 to form the mantle layer 12 by methods known in the art. Of course, other methods known in the art may be used to envelop the mantle layer 12 about the metal core 11, so long as the mantle layer 12 can be substantially uniformly placed about the core 11.

Once the mantle layer 12 has been put in place, a cover 13 may be positioned about the mantle layer 12. In an embodiment, a material that can be easily textured may be used as cover 13, so that subsequent to its placement about the mantle layer 12, the cover 13 can be imprinted with an aerodynamically optimized pattern.

The design of the golf ball of the present invention and the materials for their construction focuses on, among other things, a balance of the material resilience (i.e., spring-like ability per unit volume), elasticity (i.e., ability to reflect energy without hysteresis loss) and compressibility (i.e., ability to undergo reversible deformation in response to pressure). By providing the golf ball 10 of the present invention with core made from a type 301 stainless steel, and a mantle layer made from a mixture of long-ball SHS and short-ball SHS, the carry distance can remain substantially uncompromised, while providing the golf ball with noticeably improved “feel.”

In an embodiment of the present invention, metal core 11, constructed from work-hardened 301 stainless steel, may be provided with a thickness of about 0.039″. In addition, the metal core 11 may be provided with a density of between about 7.8 and about 8.1 and a diameter between about 0.9″ and 1.1″.

The mantle layer 12, on the other hand, may be fabricated with an inner diameter substantially equal to the outer diameter of metal core 11, and an outer diameter of about 1.550″. The cover layer 13, as noted above, may be patterned and may have a thickness from about 0.05″ to about 0.75″. In an embodiment, cover layer 13 may have a thickness of about 0.0625″. The mantle layer 12 and the cover layer 13 may together have a density of about 0.96.

The weight of golf ball 10 may be adjusted, in an embodiment, by changing the thickness of the metal core 11. Moreover, the mantle layer 12, which when formed from a mixture of long-ball resin and soft-ball resin as golf-ball sized neat spheres, has a COR of at least 0.800 and a Comp ranging from about 60 to about 63.

While the invention has been described in connection with the specific embodiments thereof, it will be understood that it is capable of further modification. Furthermore, this application is intended to cover any variations, uses, or adaptations of the invention, including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains. 

1. A golf ball comprising: a core made from a metal alloy; a mantle layer enveloping the metal core, the mantle layer including a mixture of a long-ball resin and a soft-ball resin, such that the amount of soft-ball resin is higher than the amount of long-ball resin; and a cover positioned about the mantle layer, so as to protect the mantle.
 2. A golf ball as set forth in claim 1, wherein the core is made from a work-hardened metal alloy.
 3. A golf ball as set forth in claim 1, wherein the core is hollow.
 4. A golf ball as set forth in claim 1, wherein the core includes two substantially similar hemisphere welded to one another.
 5. A golf ball as set forth in claim 1, wherein the metal alloy from which the metal core is made includes iron, nickel, chromium, carbon, silicon, and manganese.
 6. A golf ball as set forth in claim 1, wherein the metal alloy from which the metal core is made includes iron, about 6-8(w/w)% nickel, about 16-18(w/w)%) chromium, and at most about 0.15(w/w)% carbon, about 1 (w/w)% silicon and about 2(w/w)% manganese.
 7. A golf ball as set forth in claim 1, wherein the metal alloy from which the metal core is made is an AISI type 301 stainless steel.
 8. A golf ball as set forth in claim 1, wherein the metal core has an outer diameter ranging from about 0.90 inches to about 1.15 inches.
 9. A golf ball as set forth in claim 1, wherein the mixture of long-ball resin and soft-ball resin in the mantle layer includes a mixture of an ethylene methylacrylic acid ionomer (Surlyn®), and an alkylene etherester terephthalic acid polymer (Hytrel®) mixed with ZnO and magnesium stearate.
 10. A golf ball as set forth in claim 1, wherein the mixture of long-ball resin and short-ball resin in the mantle layer has a mixture ratio of about 2:3, long-ball resin to soft-ball resin.
 11. A golf ball as set forth in claim 1, wherein the long-ball resin is HPF 2000®.
 12. A golf ball as set forth in claim 1, wherein the soft-ball resin is AD
 1035. 13. A golf ball as set forth in claim 1, wherein the mantle layer has a COR ranging from about 0.800 to about 0.826.
 14. A golf ball as set forth in claim 1, wherein the mantle layer has a Comp ranging from about 91 to about
 93. 15. A golf ball as set forth in claim 1, wherein the cover has a thickness ranging from about 0.05”to about 0.75”.
 16. A method for manufacturing a golf ball, the method comprising: providing a core made from a metal alloy; enveloping the metal core with a mantle layer made from a mixture of a long-ball resin and a soft-ball resin, wherein the amount of soft-ball resin is relatively higher than the amount of long-ball resin; and placing a cover about the mantle layer, so as to protect the mantle.
 17. A method as set forth in claim 16, wherein the step of providing includes providing two substantially similar hemisphere from which the core can be made.
 18. (canceled)
 19. A method as set forth in claim 16, wherein the step of providing includes welding to one another two substantially similar hemispheres stamped from work-hardened metal alloy.
 20. A method as set forth in claim 16, wherein, in the step of providing, the metal core has outer diameter ranging from about 0.90 inches to about 1.15 inches.
 21. A method as set forth in claim 16, wherein, in the step of providing, the metal alloy from which the metal core is made is an AISI type 301 stainless steel.
 22. A method as set forth in claim 16, wherein the step of enveloping includes injection molding the mantle layer about the metal core.
 23. A method as set forth in claim 16, wherein the step of enveloping includes providing the mixture of long-ball resin and short-ball resin in the mantle layer with a mixture ratio of about 2:3, long-ball resin to soft-ball resin.
 24. A method as set forth in claim 16, wherein the step of enveloping includes providing the mantle layer with a COR ranging from about 0.820 to about 0.826.
 25. A method as set forth in claim 16, wherein the step of enveloping includes providing the mantle layer with a Comp ranging from about 60 to about
 93. 26. A method as set forth in claim 16, wherein the step of placing includes providing the cover with a thickness ranging from about 0.05”to about 0.75”. 